Regulation of globular adiponectin-induced apoptosis by reactive oxygen/nitrogen species in RAW264 macrophages

Adiponectin, produced predominantly by differentiating adipocytes, is a protein hormone with antidiabetic and immunosuppressive properties. Here, we report evidence that treatment with globular adiponectin (gAd) induces apoptosis in murine macrophage-like RAW264 cells through the generation of reactive oxygen and/or nitrogen species (ROS/RNS). Treatment with gAd induced apoptosis and enhanced the activities of caspase-3 and -9, but not caspase-8. The gAd stimulation increased ROS generation and significantly reduced the ratio of NADPH to total NADP. Pretreatment with diphenyleneiodonium or apocynin reduced ROS and apoptosis in gAd-treated cells. In addition, transfection with p47^phox- or gp91^phox-specific small interfering RNA (siRNA) partially reduced ROS and apoptosis in response to gAd treatment. These results suggest that the administration of gAd induces apoptosis after ROS generation involving activation of NADPH oxidases. The gAd stimulation increased the release of NO into the culture medium, the activity of nitric oxide synthase (NOS), and the expression of inducible NOS (iNOS) mRNA in RAW264 cells. l-NAME reduced gAd-induced apoptotic cell death. In addition, transfection with an iNOS-specific siRNA markedly reduced the generation of NO and the population of apoptotic cells. Taken together, these results demonstrate that the gAd-induced apoptotic process in RAW264 cells involves ROS and RNS, which are generated by NADPH oxidases and iNOS, respectively.